1. Field of the Invention
The present invention is related with an apparatus for reproducing information of an information record medium such as an optical disk, on which the information is recorded magnetically or by means of a phase pit and the like, and in which an information record layer is formed in multiple layers or a one-layer. The present invention is also related with an apparatus for automatically setting, in the reproducing apparatus for reproducing the multiple-layer disk, each loop gain value and/or equalizer value in a focus servo and a tracking servo, and a level value and/or an equalizer value in an RF (Radio Frequency) signal, which are optimal for each layer.
2. Description of the Related Art
Recently, DVD (Digital Video or Versatile Disk) has been remarkably developed which dramatically improves a memory density over a conventional CD and services as a high density record medium that can record one movie and the like.
Although this DVD has a different disk substrate thickness from the CD, the principle of reading a record pit responsible for storing information is similar to that of the CD. Thus, a CD/DVD compatible type of a reproducing apparatus may be proposed. In this CD/DVD compatible type of the reproducing apparatus, in order to optimally collect an information recording beam on an information record surface of each disk, it is considered to employ a bifocal lens that can emit two light beams focused on different positions on one straight line, or a method of exchanging lenses so as to change a focal length in corresponding with the type of the disk, or other methods.
Incidentally, in the DVD, it is prescribed that a linear velocity thereof is higher than that of the CD from a request of making a density higher. So, it is necessary that servo gains and servo frequency bands in focus and tracking servo circuits are made different between the CD and the DVD. More actually, the DVD is set to be wider in servo band on a high frequency side than the CD. The DVD is set to be larger in servo gain than the CD.
Therefore, in order to share the servo circuit between the CD and the DVD in the CD/DVD compatible type of the reproducing apparatus, it is necessary to adjust the servo gain and the servo band based on the disk. Namely, prior to a reproduction operation, it is judged whether or not an optical disk to be reproduced is the CD or the DVD. The servo gain and the servo band for the disk are correctly adjusted on the basis of a signal indicative of a reflectance factor of the optical disk based on the judged result, for example, the S-shaped signal of the focus error, an RF signal or the like. The once adjusted value is maintained until the disk is exchanged.
There are a single layer disk, where an information record surface on which a pit responsible for recording the information is recorded is composed of a single layer, and a multiple-layer disk having a plurality of record layers (for example, two layers) within a same thickness portion, in the DVD. In a case of the multiple-layer disk, there is, for example, such a problem that if a gain set for a record layer of a first layer in a two-layer disk is used for a record layer in a second layer as it is, the optimization is not performed at the record layer in the second layer, because of a relative slope between the respective record layers, different reflectance factors of the respective record layers, and other reasons. To solve this problem, it is enough to perform a setting operation of the gain on the basis of the focus error signal and the like so as to set to a gain corresponding to the record layer at the jump destination, each time the reading beam is jumped from the record layer in the first layer to the record layer in the second layer during reproducing or from the record layer in the second layer to the record layer in the first layer. However, in this case, initial setting for the gain and the band should be carried out each time the jump operation between the layers is performed. This results in a problem that the jump operation takes a long time to complete. Therefore, in a case of recording a series of related information, such as movies or the like, over two layers, the jump operation between the layers causes a continuous reproduction to be interrupted.
In this manner, there is a first problem in the above mentioned reproducing apparatus.
On the other hand, to reproduce the DVD, an apparatus is used which comprises an optical pickup for collecting light beams on a focus position of an information record layer of the DVD and keeps a distance between an object lens of the optical pickup and the information record layer constant by using a focus servo control, to stably read the information.
Here since an area in which a servo error signal can be detected is narrow in this focus servo control, a so-called focus search operation is required. In this focus search operation, prior to performing the focus servo control, a servo loop is made open, the objective lens is moved by a predetermined amount in a direction vertical to the information record layer, and a zero cross of a focus error signal (S-shaped signal) outputted at that time is checked, and thereby the servo loop is made close.
However, in case of the DVD of the multiple-layer disk type, since the information record layer is composed of multiple layers so as to record much information, it is required to perform the focus search operation for each layer, to reproduce such a multiple-layer disk from one side thereof.
That is, in a case of the multiple-layer disk type of the reproducing apparatus, it is necessary to jump the objective lens of the optical pickup to an appropriate position, each time the information record layer to be reproduced is switched. However, since intervals between the respective information record layers are different from each other in the respective disks within a disk standard, it is not possible to unconditionally set the jump amount. Thus, a standard position for the focus servo must be set by performing the focus search operation for each disk and each layer.
Therefore, in a case of the conventional apparatus for performing the focus search operation, it is necessary to detect the zero cross of the focus error signal each time the information record layers are switched. As a result, it is difficult to quickly switch between the information record layers in the multiple-layer DVD.
In this manner, there is a second problem in the above mentioned reproducing apparatus.